Technical Field
The present invention relates to a fixing device and an image-forming apparatus using the same.
Background Art
An image-forming apparatus of an electrophotographic system having multifunction such as a printer, a copier, a facsimile and the like has been widely known in the past. The image-forming apparatus has formed an image on a sheet through a series of processes such that the image has been transferred to the sheet and then, the image has been fixed on the sheet. The image-forming apparatus has been provided with a fixing device that performs a fixing process. The fixing device has a fixing heater(s) for performing a heat transfer on the sheet. As the fixing heater, for example, a halogen lamp can be used.
In the image-forming apparatus, an energy-saving (reduction of power consumption) has been requested in recent years. In order to realize the energy-saving of the image-forming apparatus, it has been known that reduction of power consumption in the fixing device is effective. Although heat capacity of the fixing device has been generally reduced in order to reduce the power consumption in the fixing device, temperature ripple of the fixing device may be increased when reducing the heat capacity of the fixing device. This may exert a great influence on fixing performance of the fixing device.
Accordingly, the power of the fixing device has been controlled in the past under a duty variable control by, for example, phase control or PWM control so that the temperature ripple of the fixing device may be decreased. It, however, is desirable that the fixing device may conform to various kinds of standards such as noise terminal voltage, harmonic distortion restraint, flicker regulation and the like in addition to the temperature ripple. As one of the methods of controlling power which are effective in conforming to these various kinds of standards, a technology has been known to control a heater to turn on or off the power thereof under an on-off pattern (s) of the heater (s) with half wave interval of AC power supply being constituted as a unit thereof.
For example, Japanese Patent Application Publication No. 2009-237070 has disclosed an image-forming apparatus wherein a fixing heater turns on or off based on a turn-on/off pattern of the fixing heater including ON intervals in which the fixing heater is to be turned on and OFF intervals in which the fixing heater is to be turned off. Either ON intervals or OFF intervals, which have smaller total number of half waves (units) in a repetition cycle, are discontinuous.
Japanese Patent Application Publication No. H09-80961 has disclosed a fixing device which supplies power to a heater so as to turn the heater on or off based on AC discontinuous driving pattern, whereby supplying the power which is less than rated power by AC continuous driving turn-on during a predetermined period of time from at least on-timing of the heater.
Japanese Patent Application Publication No. H11-344899 has disclosed a fixing device in which a control device selects one of a plurality of specified periods in accordance with duration of specified periods and then, controls the switching of switching device during the selected specified periods.